dns-rpz
BIND Domain Name Service Response Policy Zone

BIND Response Policy Zones

By
on
June 10, 2020

Domain Name Service

Accessing resources across the internet is done through the use of IP addresses. When trying to access your email, Google for searching, or your favorite social media outlet, you are making a connection to the their IP address. The Domain Name Service (DNS) converts a name to an IP, allowing you to easily remember your favorite website. For instance, DNS will covert www.amazon.com to 89.187.178.56. How could we use BIND and DNS to thwart the bad guys?

Response Policy Zones

One of the best, unknown features of BIND is its use of Response Policy Zones (RPZ). RPZ’s allow an administrator to re-write a DNS query and send it back to the user. In the example above, when a user goes to access Amazon, DNS converts a name to a number. Once the web browser knows that number, it then reaches out to the server to access its resources. What if we were to manipulate that number, or make it where Amazon did not exist to our users?

This is where the functionality of RPZ’s come in. By configuring BIND to receive a DNS recursive lookup and manipulate the response back to the user, you can effectively stop users from accessing malicious sites.

Let us look at the recent privacy and security concerns related to Zoom. Due to its popularity and ease of use, the Zoom video conferencing service has not become a front runner. Not only has Zoombombing, where an uninvited user gains access to your video sharing stream, become a headache for the service but so has phishing websites. Recently, URL’s listed as zoompanel.com and zoomdirect.com.au have sprung up. These websites are used to phish a users Zoom credentials. We can use RPZ’s to block company personnel or home users from accessing those websites, mitigating the attack.

How Do RPZ’s Work?

rpz-hidden-master

When properly configured, a BIND RPZ file will return a different IP address than the one that is published on the internet. The following will return a valid IP address for zoomdirect.com.au.

nslookup zoomdirect.com.au 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53


Non-authoritative answer:
Name: zoomdirect.com.au
Address: 119.81.45.82

The query responded with the IP address of 119.81.45.82.

What does a RPZ response look like?

nslookup zoomdirect.com.au ns1.svarthal.net
Server: ns1.svarthal.net
Address: 45.19.203.68#53

** server can’t find zoomdirect.com.au: NXDOMAIN

From the example above, the response changed from 119.81.45.82 to NXDOMAIN. This means that the response came back with nothing, making the phish server non-existent.

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